The present invention relates to a membrane stack unit for multichamber processes, the unit being of the type including sealing frames, end plates and membranes provided at oppositely disposed sides of the sealing frame to define chambers. Corresponding supply and connecting bores for solutions to be treated are in communication with the interior of the chambers along the sealing frame, alternatingly via inlet and outlet channels. The invention further relates to uses of such a unit.
The principle of electrodialysis, the configuration of a membrane stack for desalinating a sodium chloride solution by means of two streams of solute, and the basic design for a sealing frame are disclosed in DE-AS [Published Application] 2,902,247. However, with this proposed design of the membrane stack it is impossible to operate multicircuit processes for the purpose of recovering substances from solutions and waste waters under economical conditions or to recycle such substances or separate environmentally harmful substances, since it does not provide for the intake and discharge of more than two solute streams and does not make such provision possible with simple means.
Laboratory apparatus is also known in which the chambers are supplied individually. However, these chambers have a thickness of 5 mm, which would lead to considerable dimensions of the membrane stack if the number of chambers is increased and to difficulties in the application of joint intake and discharge conduits.
If up to four separate streams are required to perform certain tasks, it is possible, in some cases, to implement the process in two successive steps with two series connected conventional membrane stacks, but the added costs are considerable due to greater expenditures for apparatus and increased energy consumption.